How do I scale down/zoom out an environment texture?
Vector Mapping node is the way.

Make sure you are using an Environment Texture node connected to the Generated socket of a Texture Coordinate node. Then use the Vector Mapping X or Y scale to control it.



Make sure you scale only in one of the three axis, otherwise it will yield no visible effect. Also have in mind that this may introduce some stretching distortion, as spherical environment textures can't really be "zoomed out" in the traditional 2D image sense.